An IP multimedia subsystem (IMS) is a functional network architecture used to facilitate the delivery of multimedia services, such as telephony over IP and video-conferencing, over an IP network. It is of particular use in cellular networks that allow users of cellular telephones to access Internet services.
Typically an IMS 10 has the architecture illustrated in FIG. 1. It has an application layer 12 that includes application servers 14. The application servers 14 host the services provided to users by the IMS 10. The application layer 12 also includes a Home Subscriber Server (HSS) 16. The HSS 16 stores information, such as identification information and subscription-related information, for each user terminal using the IMS 10. In one embodiment, HSS 16 is the master database for the IMS network. HSS 16 may be include one or more physical database. For example, a physical database may be implemented using physical storage, e.g., non-transitory computer readable media.
The IMS layer 18 is responsible for media and session control within the IMS 10. It includes Call Session Control Functions (CSCF) which establish, monitor, support and release multimedia sessions. The CSCFs also manage service interactions for each user within the IMS. A CSCF may be a Serving-CSCF (S-CSCF) 20, Proxy-CSCF (P-CSCF) 22 or an Interrogating-CSCF (I-CSCF) 24 and is preferably a SIP server.
The S-CSCF 20 is located within the network controlled by the HSS 16, also known as the home network, and stores the details of user terminals accessing services in the home network. It controls communication sessions within the IMS 10 by invoking an application server 14 that can provide a service in response to a request from a user terminal for the service. The P-CSCF 22 is assigned to a terminal when it registers with a network and becomes the contact point of the terminal. The P-CSCF 22 can be in either the home network of the terminal or the visiting network. The I-CSCF 24 provides a gateway between different IMS 10 and enables topology hiding and the use of multiple S-CSCF 20 in an IMS 10.
Finally, the transport layer 26 enables a user terminal 28 to access the IMS 10. It includes user terminals such as cellular telephones 28 and may also include, among other components, gateways (not shown) to allow non IMS-compatible systems, such as VoIP systems, to access the IMS 10.
As will be known by one skilled in the art the components present in the IMS are not limited to those described above.
In order to access a service a user will cause a user terminal 28 to request a service. The request is routed through to the S-CSCF 20. The S-CSCF 20 authenticates the user identity of the user terminal 28 with the HSS 16 in the home network and, if the service can be provided, forwards the request to an application server 14. The application server 14 can then provide the service to the user terminal 28. All messages exchanged between the application server 14 and the user terminal 28 are passed through the S-CSCF 20.
When a user terminal 28 initially registers and authenticates a user identity in an IMS 10, the S-CSCF 20 downloads authentication vectors from the HSS 16 and performs the authentication of the user terminal 28. If the user terminal 28 is successfully authenticated, the S-CSCF 20 downloads, from the HSS 16, the user profile associated with the user terminal's 28 user identity.
After initial registration, the user terminal 28 may re-register, but the HSS 16 may not be contacted for this re-registration. This is because the user terminal 28 is doing a periodic refresh of its registration status and there is no need to re-authenticate the user terminal 28 again, nor download a fresh user profile from the HSS 16. This means that if the HSS 16 is reset, for example because of a hardware upgrade data, inaccuracies may occur. Hence, what is needed is a method for improving the integrity of the subscriber data in the event of an HSS Reset.